Alcohol intake is linked to lower sperm quality, according to a cross-sectional study of young Danish men published online October 2 in BMJ Open.

Beth Skwarecki, Medscape, Oct 15, 2014

Adverse effects on semen can be seen at levels as low as five drinks per week, although the trend is more pronounced among men who drink more than 25 units per week, the researchers report. However, at least one expert remains unconvinced of the association.

Tina Kold Jensen, MD, from the Department of Environmental Medicine, University of Southern Denmark, and colleagues, enrolled 1221 Danish men being examined for military draft, aged 18 to 28 years, who filled out a questionnaire about alcohol consumption as part of their examination and who were willing to provide a semen sample. The participation rate was 30%.

The men's average alcohol intake in the previous week was 11 units, where a unit is defined as 25 g of ethanol, the approximate amount in one beer or one glass of wine. Sixty-four percent of the participants reported binge drinking twice or more in the previous 30 days, and 45% said their recent intake was typical.

For men who said their recent intake was typical, investigators found an inverse dose-response relationship with sperm concentration (P trend = .02), as well as with total sperm count (P trend = .01) and percentage morphologically normal sperm (P trend = .01). The trends were more pronounced among men who drank more than 25 units of alcohol in a typical week.

Men who drank more than 40 units per week had an average sperm concentration of 33 million/mL compared with 50 million/mL for men drinking from one to five units a week. Percentage of abnormal sperm, based on the World Health Organization criteria, ranged from 7.8% normal among men drinking from zero to five units to 6.5% among men drinking more than 40 units a week.

The association did not hold for participants who said their recent intake was not typical, which the researchers note was expected, as sperm take 72 days to mature. Hormone concentrations, however, can respond more rapidly, and in fact, recent alcohol intake and more frequent bingeing in the previous month were associated with higher concentrations of testosterone and lower concentrations of sex hormone-binding globulin.

Participants who had consumed more than 30 units in the previous week were more likely to also be smokers, had a higher caffeine intake, and were more likely to report sexually transmitted infections. The investigators did not find an independent relationship between binge drinking and sperm quality, but noted that participants who binged also tended to have higher alcohol intake in general. The investigators write that "the negative association between alcohol intake and semen quality may be attributed to a direct adverse effect of alcohol on spermatogenesis or it may be a result of differences in lifestyle, health behaviour and diet found among high alcohol consumers, despite adjustment for these factors."

"Interpreting the results from this study can be tricky," Jorge Chavarro, MD, ScD, from the Harvard School of Public Health, Boston, Massachusetts, told Medscape Medical News. Dr Chavarro was not involved in the work but regularly collaborates with the authors. He noted that although the downward trend in sperm concentration is statistically significant, the individual values at each level were not significantly different from the reference category of one to five units. "For me, the tiebreaker really comes down to putting these new findings in the context of the existing literature," he said, including a recent meta-analysis that showed no relation between alcohol intake and semen quality.

He added, "My guess is that if these two recent papers were added to a new meta-analysis, the conclusion would be of no relation again. I think the most innovative contribution of this paper was the report on alcohol binging, which, to my knowledge, nobody had previously addressed."